Two novel nonlinear companding schemes with iterative receiver to reduce PAPR in multi-carrier modulation systems

Companding transform is an efficient and simple method to reduce the Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Modulation (MCM) systems. But if the MCM signal is only simply operated by inverse companding transform at the receiver, the resultant spectrum may exhibit severe in-band and out-of-band radiation of the distortion components, and considerable peak regrowth by excessive channel noises etc. In order to prevent these problems from occurring, in this paper, two novel nonlinear companding schemes with a iterative receiver are proposed to reduce the PAPR. By transforming the amplitude or power of the original MCM signals into uniform distributed signals, the novel schemes can effectively reduce PAPR for different modulation formats and sub-carrier sizes. Despite moderate complexity increasing at the receiver, but it is especially suitable to be combined with iterative channel estimation. Computer simulation results show that the proposed schemes can offer good system performances without any bandwidth expansion

Analysis of MAC-level throughput in LTE systems with link rate adaptation and HARQ protocols

LTE is rapidly gaining momentum for building future 4G cellular systems, and real operational networks are under deployment worldwide. To achieve high throughput performance, in addition to an advanced physical layer design LTE exploits a combination of sophisticated mechanisms at the radio resource management layer. Clearly, this makes difficult to develop analytical tools to accurately assess and optimise the user perceived throughput under realistic channel assumptions. Thus, most existing studies focus only on link-layer throughput or consider individual mechanisms in isolation. The main contribution of this paper is a unified modelling framework of the MAC-level downlink throughput of a sigle LTE cell, which caters for wideband CQI feedback schemes, AMC and HARQ protocols as defined in the LTE standard. We have validated the accuracy of the proposed model through detailed LTE simulations carried out with the ns-3 simulator extended with the LENA module for LTE

[[alternative]]System Evaluation, Simulation Platform Set Up and Baseband Circuit Implementation for Wireless Sensor Network

計畫編號：NSC93-2213-E032-023研究期間：200408~200507研究經費：515,000[[abstract]]本計畫分三年以實現無線感測網路之系統評估模擬平台建置與基頻電路研製。本計劃研 究子題如下： (A) IEEE 802.15.4 系統之分析及設計 1. 媒介擷取控制層與實體層間之介面設計 2. 系統架構的確定，系統規格及各子方塊之間之介面規格之訂定 3. 低功率基頻電路的設計及探討 4. 接收機技術研究(同步、通道等化、信號偵測等) 5. 利用 ADS 與 Matlab 以建立模擬平台 6. 傳送端與接收端低功率基頻電路之硬體實現 (B) IEEE 802.15.4a 系統之分析及設計 1. UWB 基本原理之研究與探討 2. UWB 傳送與接收基本技術之研究 3. 利用 ADS 及 Matlab 建立模擬平台，對 UWB 之架構模擬 4. UWB 基本方塊規格之訂定 5. 精確定位之研究 (C) IEEE 802.15.4 之MIMO 架構設計 1. MIMO 架構之演算法與架構之研究 2. MIMO 架構之用於IEEE 802.15.4 之通道效應之探討與研究 3. 利用MIMO 架構傳送MPEG-4 之效能探討 4. MIMO 架構之接收技術之研究 5. 利用 ADS 及 Matlab 建立性模擬平台以研究多頻帶的傳輸特性 6. 探討如何利用基頻電路的切換以達低功率而高速的信號傳送 (D) 通道分析及模型的建立 1. 通道傳送損失特性之分析 2. 路徑衰減及多重路徑之分析 3. 路徑衰減之經驗公式推導 4. 通道模型之建立 5. 通道等化器演算法之推導及分析(E) 模擬平台的建立 1. 利用 ADS 程式以建立基頻及 RF 端之模擬平台 2. 利用 Matlab 程式以建立基頻及 RF 端之模擬平台 3. 基頻及 RF 端 ADS 模擬平台的介面設計 4. 基頻及 RF 端 Matlab 模擬平台的介面設計 5. 系統特性的模擬及數據分析 (F) 測試平台的建立 1. IEEE 802.15.4 實體層各子方塊之 Verilog 程式燒錄至 FPGA 並測試 2. IEEE 802.15.4 實體層整合電路之 Verilog 程式燒錄至 FPGA 並測試 3. Mulit-Band 實體層之 Verilog 程式燒錄至 FPGA 並測試 4. IEEE 802.15.4 實體層 ASIC 之測試 5. IEEE 802.15.4 實體層 ASIC 與 RF 之整合測試 6. IEEE 802.15.4 實體層 ASIC 與 MAC 之整合測試 7. IEEE 802.15.4 實體層 ASIC , MAC 及 RF 之整合測試[[sponsorship]]行政院國家科學委員

Transmit antenna subset selection with power balancing for high data rate MIMO-OFDM UWB systems

This paper proposes per-subcarrier transmit antenna subset selection with power balancing for MIMO-OFDM UWB systems to simultaneously improve the system error performance and increase data rates. The deployment of the per-subcarrier antenna subset selection may result in a power unbalance across antennas, which could cause power amplifiers (PAs) to operate in their non-linear regions. To overcome this disadvantage, we formulate a linear optimization problem for the optimal allocation of data subcarriers under a constraint that all antennas have the same number of assigned data symbols. This optimization problem could be applied to systems with an arbitrary number of multiplexed data streams, antennas, and with different selection criteria. The efficacy of the proposed allocation scheme from the PA linearity perspective is validated by analyzing the distribution of the peak amplitude of timedomain signals. Simulation results demonstrate that the proposed system outperforms the system without a balancing constraint

Theoretical Analysis and Performance Comparison of multi-carrier Waveforms for 5G Wireless Applications

5G wireless technology is a new wireless communication system that must meet different complementary needs: high data rate for mobile services, low energy consumption and long-range for connected objects, low latency to ensure real-time communication for critical applications and high spectral efficiency to improve the overall system capacity. The waveforms and associated signals processing, present a real challenge in the implementation for each generation of wireless communication networks. This paper presents the diverse waveforms candidate for 5G systems, including: CE-OFDM (Constant Envelope OFDM), Filter-Bank Multi Carrier (FBMC), Universal Filtered Multi-Carrier (UFMC) and Filtered OFDM (F-OFDM). In this work, simulations are carried out in order to compare the performance of the OFDM, CE-OFDM, F-OFDM, UFMC and FBMC in terms of Power spectral density (PSD) and of Bit Error Rate (BER). It has been demonstrated that (CE-OFDM), constitutes a more efficient solution in terms of energy consumption than OFDM signal. Moreover, the (F-OFDM), (UFMC) and (FBMC) could constitute a more efficient solution in terms of power spectral density, spectral efficiency and bit error rates. In fact, CE-OFDM reduces the Peak to Average Power Ratio (PAPR) associated with OFDM system, FBMC is a method of improving out-of-band (OOB) characteristic by filtering each subcarrier and resisting the inter-carrier interference (ICI). While, UFMC offers a high spectral efficiency compared to OFDM

Multiuser equalizer for hybrid massive MIMO mmWave CE-OFDM systems

This paper considers a multiuser broadband uplink massive multiple input multiple output (MIMO) millimeter-wave (mmWave) system. The constant envelope orthogonal frequency division multiplexing (CE-OFDM) is adopted as a modulation technique to allow an efficient power amplification, fundamental for mmWave based systems. Furthermore, a hybrid architecture is considered at the user terminals (UTs) and base station (BS) to reduce the high cost and power consumption required by a full-digital architecture, which has a radio frequency (RF) chain per antenna. Both the design of the UT’s precoder and base station equalizer are considered in this work. With the aim of maximizing the beamforming gain between each UT and the BS, the precoder analog coefficients are computed as a function of the average angles of departure (AoD), which are assumed to be known at the UTs. At the BS, the analog part is derived by assuming a system with no multi-user interference. Then, a per carrier basis nonlinear/iterative multi-user equalizer, based on the iterative block decision feedback equalization (IB-DFE) principle is designed, to explicitly remove both the multi-user and residual inter carrier interferences, not tackled in the analog part. The equalizer design metric is the sum of the mean square error (MSE) of all subcarriers, whose minimization is shown to be equivalent to the minimization of a weighted error between the hybrid and the full digital equalizer matrices. The results show that the proposed hybrid multi-user equalizer has a performance close to the fully digital counterpart.publishe

Técnicas de igualização adaptativas com estimativas imperfeitas do canal para os futuros sistemas 5G

Wireless communication networks have been continuously experiencing an exponential growth since their inception. The overwhelming demand for high data rates, support of a large number of users while mitigating disruptive interference are the constant research focus and it has led to the creation of new technologies and efficient techniques. Orthogonal frequency division multiplexing (OFDM) is the most common example of a technology that has come to the fore in this past decade as it provided a simple and generally ideal platform for wireless data transmission. It’s drawback of a rather high peak-to-average power ratio (PAPR) and sensitivity to phase noise, which in turn led to the adoption of alternative techniques, such as the single carrier systems with frequency domain equalization (SC-FDE) or the multi carrier systems with code division multiple access (MC-CDMA), but the nonlinear Frequency Domain Equalizers (FDE) have been of special note due to their improved performance. From these, the Iterative Block Decision Feedback Equalizer (IB-DFE) has proven itself especially promising due to its compatibility with space diversity, MIMO systems and CDMA schemes. However, the IB-DFE requires the system to have constant knowledge of the communication channel properties, that is, to have constantly perfect Channel State Information (CSI), which is both unrealistic and impractical to implement. In this dissertation we shall design an altered IB-DFE receiver that is able to properly detect signals from SC-FDMA based transmitters, even with constantly erroneous channel states. The results shall demonstrate that the proposed equalization scheme is robust to imperfect CSI (I-CSI) situations, since its performance is constantly close to the perfect CSI case, within just a few iterations.Redes sem fios têm crescido de maneira contínua e exponencial desde a sua incepção. A tremenda exigência para altas taxas de dados e o suporte para um elevado número de utilizadores sem aumentar a interferência disruptiva originada por estes são alguns dos focos que levaram ao desenvolvimento de técnicas de compensação e novas tecnologias. “Orthogonal frequency division multiplexing” (OFDM) é um dos exemplos de tecnologias que se destacaram nesta última década, visto ter fornecido uma plataforma para transmissão de dados sem-fio eficaz e simples. O seu maior problema é a alta “peak-to-average power ratio” (PAPR) e a sua sensibilidade a ruído de fase que deram motivo à adoção de técnicas alternativas, tais como os sistemas “single carrier” com “frequency domain equalization” (SC-FDE) ou os sistemas “multi-carrier” com “code division multiple access” (MC-CDMA), mas equalizadores não lineares no domínio de frequência têm sido alvo de especial atenção devido ao seu melhor desempenho. Destes, o “iterative block decision feedback equalizer” (IB-DFE) tem-se provado especialmente promissor devido à sua compatibilidade com técnicas de diversidade no espaço, sistemas MIMO e esquemas CDMA. No entanto, IB-DFE requer que o sistema tenha constante conhecimento das propriedades dos canais usados, ou seja, necessita de ter perfeito “channel state information” (CSI) constantemente, o que é tanto irrealista como impossível de implementar. Nesta dissertação iremos projetar um recetor IB-DFE alterado de forma a conseguir detetar sinais dum transmissor baseado em tecnologia SC-FDMA, mesmo com a informação de estado de canal errada. Os resultados irão então demonstrar que o novo esquema de equalização proposto é robusto para situações de CSI imperfeito (I-CSI), visto que o seu desempenho se mantém próximo dos valores esperados para CSI perfeito, em apenas algumas iterações.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Performance evaluation of T-transform based OFDM in underwater acoustic channels

PhD ThesisRecently there has been an increasing trend towards the implementation of orthogonal frequency division multiplexing (OFDM) based multicarrier communication systems in underwater acoustic communications. By dividing the available bandwidth into multiple sub-bands, OFDM systems enable reliable transmission over long range dispersive channels. However OFDM is prone to impairments such as severe frequency selective fading channels, motioned induced Doppler shift and high peak-to-average-power ratio (PAPR). In order to fully exploit the potential of OFDM in UWA channels, those issues have received a great deal of attention in recent research. With the aim of improving OFDM's performance in UWA channels, a T-transformed based OFDM system is introduced using a low computational complexity T-transform that combines the Walsh-Hadamard transform (WHT) and the discrete Fourier transform (DFT) into a single fast orthonormal unitary transform. Through real-world experiment, performance comparison between the proposed T-OFDM system and conventional OFDM system revealed that T-OFDM performs better than OFDM with high code rate in frequency selective fading channels. Furthermore, investigation of different equalizer techniques have shown that the limitation of ZF equalizers affect the T-OFDM more (one bad equalizer coefficient affects all symbols) and so developed a modified ZF equalizer with outlier detection which provides major performance gain without excessive computation load. Lastly, investigation of PAPR reduction methods delineated that T-OFDM has inherently lower PAPR and it is also far more tolerant of distortions introduced by the simple clipping method. As a result, lower PAPR can be achieved with minimal overhead and so outperforming OFDM for a given power limit at the transmitter